A MEMS microphone serves to convert voice signals into electrical signals, and is manufactured by using a semiconductor batch process.
Compared to an electret condenser microphone (ECM) applied to most automotive vehicles, the MEMS microphone has excellent sensitivity and low performance variation per product, and can be ultra-miniaturized and strong against environmental changes such as heat, humidity, etc. As a result, development has recently been carried out in a direction of replacing the ECM with the MEMS microphone.
The MEMS microphone is classified into an electrostatic capacitive MEMS microphone and a piezoelectric MEMS microphone.
The electrostatic capacitive MEMS microphone includes a fixed membrane and a vibration membrane, and when a sound pressure (sound source) is applied from outside to the vibration membrane, a capacitance value varies as a distance between the fixed membrane and the vibration membrane varies. A thus-generated electric signal is used to measure a sound pressure.
For example, the electrostatic capacitive MEMS microphone measures a change in capacitance between the vibration membrane and the fixed membrane and outputs it as a voltage signal, i.e., sensitivity, which is one of the most important performance indexes of MEMS microphones.
Meanwhile, a technique to reduce rigidity of the vibration membrane is required in order to improve the sensitivity which is the major performance index of the MEMS microphone. To that end, a method of lowering residual stress of the vibration membrane, applying a spring structure, or the like has conventionally been developed.
For example, FIGS. 1A and 1B illustrate a vibrating membrane structure to which a slot pattern and a spring pattern are applied in order to improve a conventional sensitivity.
First, referring to FIG. 1A, a technique of reducing the rigidity by forming a slot pattern in a vibration membrane and increasing a slot length has been developed in the prior art in order to improve the sensitivity of the MEMS microphone.
However, according to the prior art, a chip size may increase to increase the slot length, and a sound source may be lost in a low band.
In addition, according to the prior art, a method of reducing a stress by applying a spring pattern to a vibration membrane has been developed, but process complexity may increase to realize a minute spring pattern in the vibration membrane, and a product yield may be lowered in an experiment, as shown in FIG. 1B.
Thus, it is urgently required to develop a new vibration membrane structure that can improve vibration displacement and robustness of the process in order to improve sensitivity, which is the major performance index of the MEMS microphone.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.